I was playing rainbow six vegas 1 multiplayer, then suddenly the screen became black, and goes back to PS3 menu. I didn't quit the game, it just did it by itself while I was playing online. Is there something wrong with my PS3? or the game?

Please tell me a guide to fix this problem.
It happen twice so far. And Im a bit worry if it happens again, and it gets in my nerves because I wont gain my exp points. T.T